Various methods and apparatus for positioning the master pattern in relation to the desired location of a printed or transfer pattern on material to be printed are known to be art.
For example, there is described in U.S. Pat. No. 4,226,181 a method and apparatus for adjusting the position of a stencil in relation to a printing table, according to which method:
(a) A transparent material is placed on the printing table, over a reference pattern; PA1 (b) The stencil master pattern is transferred to the transparent material, through a printing process; PA1 (c) Any deviation between the printed pattern and the reference pattern is compensated for and eliminated by displacing the printed transparent material in a manner to cause the printed pattern to coincide with the reference pattern; PA1 (d) The positions of the stencil and the stencil frame are adjusted in precisely the same manner as the position of the transparent material. PA1 (a) Positioning a reference pattern, serving as a master pattern, on an alignment table separate from the printing table and creating a first reference pattern alignment means corresponded by second alignment or index means on the printing machine; PA1 (b) Scanning the reference pattern formed on the master pattern to establish pre-determined markings, using at least one scanning and sensing means; PA1 (c) Reading the positional values of the markings obtained with the aid of at least one scanning and sensing means; PA1 (d) Applying print in the printing machine to material registered therein with the aid of the second alignment or index means; PA1 (e) Bringing the material printed in accordance with (d) into register with the first aligning means on the alignment table; PA1 (f) Scanning the material printed according to (d) and reading markings on the print corresponding to the pre-determined markings on the reference pattern, using to this end at least one scanning and sensing means; PA1 (g) Reading the positional references of the markings on the print obtained from at least one scanning and sensing means; PA1 (h) Comparing the positional references established in accordance with steps (c) and (g); PA1 (i) Establishing each deviation between the markings of the reference pattern and the print with respect to its numerical values and directional sense; PA1 (j) Establishing displacement values suitable for rectifying this deviation and for applying subsequent print to further material substantially precisely in relation to the reference pattern; PA1 (k) Establishing the displacement values which need to be applied to a number of positioning means in order to compensate for this deviation. PA1 Establishment of the true position of the material to be printed, including small tolerances (less than 0.1 mm) when the material occupies its registered or aligned position in a printing station (on a printing table), by sensing the position of an index mark or a significant part of a previously printed pattern. PA1 Determination of the position of the aligned index mark in relation to a fixed reference, normally a location on the frame structure of the silkscreen printer. PA1 Conversion of data relating to the configuration of the index mark and obtained in time sequence. PA1 Application of measures for deriving from this sequential data unequivocal information relating to the true position of the index mark and its configuration. PA1 Establishment of the center of gravity of the index mark. PA1 Comparison of calculated x and y co-ordinates of the center of gravity of the index mark with previously stored co-ordinate reference values. PA1 Establishment of possible deviations between the center of gravity of the index mark and the stored co-ordinate values with respect to magnitude and direction. PA1 Calculation of the composite motion required of a plurality of stepping-drive motors, normally three in number, in order to compensate for the established deviation and to move either the material or the stencil to a desired position. PA1 A necessary effectuation of similar compensation with respect to a discrepancy or deviation in which the distance between two index marks differs from the same distance for the stored co-ordinate values. PA1 Provision to the stepping-motors of control signals produced in reponse to calculations carried out while observing possible compensation.
A development of the method and apparatus described in the aforesaid U.S. Pat. Specification is described in Swedish Patent Application No. 7903516-8 (corresponding to U.S. Pat. No. 4,485,447), this further development relating to adjustment of print applied to material by means of a printing machine, so that the print coincides substantially with a reference pattern. The method described in this prior Patent Application comprises
The method according to German Offenlegungsschriften No. 3 027 717 for guiding a printing arrangement with the aid of individually controllable means also forms part of the pertinent prior art.